Tube testing apparatus



Dec. 27, 1949 BURCHELL 2,492,733

TUBE TESTING APPARATUS Filed Dec. 26, 1947 Figl.

ELEMENT SWITCH BANK ELECTOR SWITCH Inventor- Robert EZBurchelh by m 6% His Attorney.

Patented Dec. 27, 1949 TUBE TESTING APPARATUS Robert E. Burchell, Syracuse, N. Y., assignor to General Electric Company, a corporation of New York Application December 26, 1947, Serial No. 793,783

6 Claims; (01. 315--364) This invention relates to tube testing a paratus and more particularly to a testing device provided with means for indicating a short circuit existing between elements of an electron discharge device.

An object of the invention is to provide testing apparatus incorporating improved short circuit indicating means.

A more particular object of the invention is to provide apparatus arranged to indicate the existence of a short circuit between elements of an electron discharge device which will test for such short circuits without subjecting thet device under test to voltages" or currents of a magnitude sufiicient to damage the device. I

A further object is to improve the sensitivit and reliability of short circuit testing apparatus for electron discharge devices.

Another object is to provide short circuit testing means which may be readily incorporated with devices and circuits for determining the condition Of electron discharge devices.

A still further object of the invention is to provide a short circuit indicating device, such as a neon lamp, which will serve the auxiliary purpose of indicating energization of the tube testing apparatus. 1

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings in which Fig. 1 is a circuit diagram of a short circuit testing circuit according to the invention, and Fig. 2 is a circuit diagram Of a complete tube testing device for providing several different tests and incorporating a short circuit testing circuit of the type shown in Fig. 1.

Turning now to Fig. 1 of the drawings, an electron discharge device I, such as is commonly referred to as a tube, is so arranged that the several elements thereof may be selectively connected through manually operated element switches to one or the other of two busses. One bus 2 is connected to one end terminal of the secondary winding 3 Of a power supply transformer and the other bus 4 is connected to a tap on winding 3 through a capacitor 5 and resistor 6 in series.

A neon lamp I is normally supplied with operating voltage at the frequency of the supply source, such as 60 cycles, being arranged in series connection with resistor 6 across the portion of the transformer secondary winding between the aforementioned end terminal and tap thereof.

In an operating equipment, the neon lamp may be one rated at about one-quarter watt, such as General Electric Company type NE-45, resistor 6 may have a resistance of 240,000 ohms and capacitor 5 a capacitance of 0.5 microfarad. The voltage provided between the aforementioned end terminal and tap is volts.

The element switches shown connected between the tube elements and respective busses permit the connection of one element, such as the anode as shown, to the upper bus 2 while all the remaining elements are connected to bus 4. With the circuit constants as outlined, leakage resistance between the anode and any one or group of the other elements which is of the order of onequarter megohm or less will cause the neon lamp to be extinguished, and it has been found that for leakage resistances up to about 400,000 ohms, there will be a noticeable decrease in intensity in the neon lamp. Operation of the element switch associated with the anode to connect it to bus 4, and of another switch, such as one associated with one of the grid elements, to connect the grid element to bus 2, will provide a short circuit or leak-age test to detect excessive leakage between the selected grid element and all of the other tube elements. Normally, each element will be tested in this manner.

In testing tubes of low current ratings, it is desirable to provide a testing circuit that can, under no conditions, damage the tube by causing excess current flow or excessive voltages. With circuit constants as shown, tthe maximum possible current through a short circuit between busses 2 and 4 will be approximately 0.00046 ampere, and thte maximum voltage on open circuit between the busses is approximately 60 volts. The result is that all types of electronic vacuum tubes in common tubes may be safet tested, and the device is additionally useful for testing devices of the type, for instance, including crystal detector diodes, metal oxide rectifiers, and thermistors Without subjecting the device to greater than rated currents.

It is to be understood that the neon lamp will glow whenever power is supplied through energization of transformer Winding 3 but will be extinguished by a short circuit between busses 2 and 4 if the resistance of the short circuit is below approximately one-quarter megoh-m, and will be of noticeably reduced intensity if the resistance of the short circuit is less than approximately 400,000 ohms,

the resistor across the portion of the winding;

from the tap mentioned to one end .terminal capacitor 5 connected in series from the neon lamp end of resistor 6 to the bus fizthrough'a switch; section to be later described, bus. 22 connected:

directly to the above mentioned end terminal of winding 3, and a plurality of tube sockets.9,,ll, ll arranged to receive tubes of various base arrangements. While three such sockets are shown, it will be understood that additional sockets will beiusuallyv desirable.- to accommodate additional types; of;' tube bases. Further flexibility. is pro,- vided; by, theincorporation into the circuits-arrangedztobe'connected to the elementsoftubes ori'other. devices tobe tested of a ,gridclip l2 ofitheusual typeand a terminal l3 which may comprise .a .jack or binding post of conventional typeiandw-hich may beused to connect one of the grid caps of a tubehaving two. gridcaps, or forrconnection to deviceswhich do not havetube base -terminals, such as thermistors. or. crystal diodes.

A group of ten individually. operable single pole four-positionelementswitches M are: provided the armatures-of eight of the switchesbeing individually-connected to th'eeight corresponde ing separate terminals of socket Q-and to-correespendin terminals of sockets H) and-ll and'ofany additional-sockets which may be provided;- Forsocketsof less than eight terminals, less-than eight switchesare, of course, so connected. ThetWo remaining switches have armatures connected togrid clip-l 2 and terminal l3 respectively. Thefour sta-tionarycontacts of each switch are con-- nected'to'--four' common busses, the first contact of-eachbeingconnected to bus l5-whichisassoc-iated with the open position of eachswitch; the second; to bus 4, which is associated-with a" switch position that may be called the normal. position; the third contact, to bus 2, correspondingto the short orleakage testposition; and thefourth to bus I6, which provides a' filament.:or heater connection. It will beapparent that each of'the elements maybe connected to any one .of the .busses by manually adjusting "the armatureto the appropriate position.

A1, multiple ganged, selector switch I1 is arrangeditoselect'the operation desired. Inthe ex treme counterclockwise position of the armatures as shown in. Fig. 2, the circuit is completed to provideafor short. circuit and leakage-tests, and in:

additionJto furnishvoltage readings-on a. suit-r ablezgalvanometer M3 .for adjusting the line volt agesettingsas laterto be described;-

The next four positions of the armatures in thesclockwisedirection complete connections for testin emission z'on, respectively, heavyi'currentr voltages of external apparatus, terminals l9 and multiplying resistors 20 being provided for this purpose.

Power transformer 8 includes a tapped primary winding with a switching arrangement for connecting a source of alternating current from the conventional dual connector plug across a desired; portion of the winding. With switch I! in itsfirst. or extreme counterclockwise position, a primary winding tap is selected which gives a desired predetermined voltage reading on meter #8, whereby iiierent supply voltages may be compensatedz For this presenting operation, the Whole secondary-filament winding 2| of the transiormeriisconnected to a series rectifying circuit including, from the upper end of the transformer secondary asshown in the drawing, a portion of" an adjustin potentiometer resistor 22, the cathoderof a rectifier tube 23, the anode of the rectifier, and a current limiting resistor 24 to the otherend of'the winding, Inan operative apparatus; a current. limiting resistor- ZA of; 68,000 ohms-has been found satisfactory for, use'ifthefull scale meter deflection is producedv by; 500 :micro+ amperesand; the secondary. winding.;.2 lgives. a totalzvoltage of approximatelylZO. volts. Under these conditions, the potentiometer resistor. 22 should be. about, 2,000 ohms: A'direct current voltage is producedacrossthe:above mentioned portion of resistor 22 which is .proportionalto the voltage of windingfl. By a. proper: presettingof the potentiometer :resistor 22;.the meter: i8: canbe made-to read half scalewhen 'theaoorrect primary winding tap is selected'for; any normalisupply. line voltage, for. instance; between: and volts-.; The meter, it1Wi11;bB3SBBII; .is: connectedrin' shunt to the above mentionedyportionzof; resistor; 22,; the other portion ofrthe resistorcbeingrin series with the meter.

Afteriuthe. supply. line voltage; adjustment; of the primary windingaha'sbeenzcompleted, the .eleq merits of far; tube whichlsiinsertedninione of the sockets 9; IO; N, or;in;anc\.ther.v similarly arranged. socket; maybe. tested for "short: circnitsor .-ex-.- cessive. leakage: by operating each armature .oi' selector switches 14 in turn to.the;contact:.conenected to bust? andthen back .touthenormalzposition :in connection :with bus 4:. If tthe. resistance between: the element: associated. with any; ones of the :armaturesand the remain'ing elementsisless than appr oximately:240.000 ohms-the: neorrdamp.

I, which is normally energized; ,wi'llloezcompletely extinguished, .or it .will .showareducediintensity ii? the resistance :is: dessthanapproximately 40 0,000. ohms. Noidamageyto the: tube;or "other device.. under :test: can 'LOCOLII, since the maximum current; that; can xfiow through a. short circuit between-. busses i -and 1.4;"iS'; approximately 0.46:3milliantpere, and; the open" circuit; voltage between the. 'bllSSBSE. is about 60 volts; In;prior;art=-testers, the-short; circuit .currentisas {much as 123;;mi1liamperesand the ;open circuit-:voltage.mayzbe'between; 100. and 200 -volts;

The .zneon vlamp 1 is energized, to. :act as iawpilota lamp; whenever thetapwswitch is iniposition; to;-

providepower. to the. primary-winding; of trans? former 8,- unless a.- low resistance is imposedacross bussesl. and 4-. There; is,,in consequence,--. an immediate. indication that. the power issbeing. suppliedand. that. the V lamp. which is to indicate:- defectivevtubes is ,in operating condition and .not burned but It has beenfound'that capacitance effects,be-.

" tween elements of tubes under test which, in

prior art testers, gave false indications of leakage are not of consequence in the present circuit.

An additional advantage realized inthe apparatus described herein is a difference in the type of glow discharge in the neon lamp in the case of a rectifying device. The neon lamp normaly comprises two electrodes, each of which is surrounded by a glow discharge on alternating current but only one of which is surrounded by a direct current discharge. By observing the discharge in the lamp when a rectifying device of known orientation is connected between the busses 2 and 4, the orientation of other rectifiers may be readily ascertained.

Emission testing of tubes may be accomplished by setting the armatures of switch bank 11 into an appropriate one of the four positions next in the clockwise direction from the supply voltage testing and short and leakage circuit testing position. The appropriate heater voltage is selected by a switch armature 25 cooperating with fixed contacts representing taps on the secondary filament winding 2|. The element switch armature connected to one end of the tube heater or filament is moved to establish, through the third associated contact, a connection to bus 2. Emission to any one or any combination of the remaining elements may now be measured on the meter l8 by leaving the armature or armatures of element switch bank It which are associated with the selected element or elements in the normal position in connection with bus 4 and by connecting the cathode or emitting element to bus 2 through its associated armature of the element switch bank. If it is desired to omit certain elements from the emission test, they may be connected to bus l5 which is open circuited. This permits the detecting of open circuits between any tube base prong of the device under test and the element which should be connected thereto. For instance, the anode, control grid and screen grid of a pentode tube may be switched to bus IE to test the emission current flow to the suppressor grid alone acting as an anode.

With the anode or collector element or elements of the tube under test connected to bus 4, and the emitter or cathode element connected to bus 2, a circuit is established from the secondary winding 3, from the top terminal as shown, the emitter element, and from a tap, shown as nearest the said top terminal, through a test switch 26, which is closed preferably against a spring bias during the test, through the left-hand section of selector switch bank I1 and thence through an indexing resistor 21 to bus 4 and the collector elements. A movable contact is preferably provided for contacting an adjustable point on resistor 21. This contact is connected directly to meter 18 for three of the four emission testing positions of the armatures of switch l1, and through a multiplier resistor 21' in the fourth position, and the other terminal of the meter is connected through suitable multiplier resistors 28 to that end of resistor 21 which is connected to bus l and thus to the anode or collector elements of the tube under test, whereby the meter is responsive to the voltage drop occurring in the adjustable portion, shown as the upper portion in the drawing, of resistor 21 and may be calibrated to indicate, in terms of emission current, whether or not the tube is satisfactory. The indexing resistor 21 is preferably adjustable by means of a calibrated pointer (not shown) to a predetermined position in accordance with the value of emission current which is exemplary of satisfactory operation for each tube tested. For testing tubes of medium or heavy emission current ratings, with the armatures of switch 11 in the second or fourth position, one or the other of load resistors 29 is connected in shunt across indexing resistor 21, whereby resistor 21 acts as a voltage divider to provide the correct voltage to meter l8. In the third position, resistor 21 is itself the load resistor, and very low current tubes may be emission tested.

One of the resistors 28 may be adjustable to permit initial adjustment of meter sensitivity to the required degree of accuracy. Like the ad'- justment of resistor 22, this adjustment once made need not be changed, and in commercial apparatus both adjustments would normally be made at the factory.

As mentioned above, the fifth clockwise position of the armatures of switch I1 is applicable for testing tubes, such as cold cathode tubes, which require a high starting voltage. In this switch position, the whole of secondary winding 3 is connected to provide a relatively high testing voltage, an additional resistor 30 being inserted in shunt to the indexing resistor 21.

In the sixth position of the armatures of switch ii bus is energized from the end terminal of secondary winding 3, through a resistor 3| and the meter is disconnected. Electron ray tubes of the types commonly employed as tuning indicators in radio receivers may now be tested by moving the armature of the element switch connected to the triode grid or other equivalent tube element, back and forth from the position establishing contact with bus [6 to that establishing contact with bus 2 to cause opening and closing of the shadow angle.

In the extreme clockwise position of the armatures of switch l1, the external voltage terminals l9 are connected to the meter in association with desired multiplier resistors 20.

While I have shown only certain preferred embodiments of my invention by way of illustration, many modifications will occur to those skilled in the art and I therefore wish to have it understood that I intend, in the appended claims, to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to. secure by Letters Patent of the United States is:

1. In apparatus for testing electron discharge devices and the like which comprise a plurality of elements, a source of voltage, a current limiting device in series between one terminal of said source and one of said elements, a connection from the other terminal of said source to another of said elements, and a normally excited indicator lamp in shunt between said elements whereby said lamp is extinguished by a short circuit between said two elements.

2. In apparatus for indicating leakage between elements of an electron discharge device, a source of voltage with two terminals, a resistor and a gaseous discharge lamp connected in series between said terminals, and a shunt circuit for said lamp comprising means for connecting selected elements of said device to opposite terminals of said lamp, whereby leakage between said oppositely connected elements bypasses current around said lamp.

3. A testing device for electron tubes, and the like, comprising a source of voltage, a plurality of connections adapted to be connected through switching means to selectableelements of a tube to be tested, means to apply voltage from said *sourcertozsaid? connectionspameter connected .to

icatingllamprexcitedby voltage from said source :tcrindicatev that voltage. is being supplied therefrom,-- and means, comprising said switching :means; for connecting. predetermined selected ;pairs of elements of said tube in shunt with said :lamp whereby :said lamp provides .a visual indication of a low resistanceexistingbetween the respective elements of said selected pair.

\ 4.:2A .testing :device. for .electron tubes, and .the like, comprising a source of voltage, current .indicatingmeans connected .to said source in a high impedancecircuit-to indicate energization .of said source, arelatively low impedance circuit in shunt with said indicator means, said low impedance circuit-including. anormally open portion,'means.adaptedto connect two electron tube terminals to respective sides of said. open portion whereby said low impedance circuit may be closed bya--leakage path between said terminals to bypass current from-rsaid indicator.

.5..-A testing device for electron tubes, and the like, comprising a plurality ofsockets adapted to complete connections from the elements of a tube-under test-to-a plurality of switch armatures, eachof-said armatures being individually movable to further complete said connections selectively to one or-the other of two conductors, means for applying an alternating voltage between said two conductors, said means comprising current limiting means, andmeans responsive to the voltage between-said. conductors {for indicating the condition of the tube under test in accord with the current leakage-between elements as selectably connected to said: respective conductors.

6. Inapparatusior testing electron discharge devicesand thelike which comprise a plurality of elements, a sourceof alternating current voltage, a current limiting device in series between one terminal of said source and one of said elements, a connection from the other terminal of said source .to another of said elements, and a normally excited indicatorlampinshunt between said elements whereby said lamp is extinguished bya short circuit between said two elements.

ROBERT. E. *BURCHELL.

REFERENCES CITED The following references are of'recordin the file of this patent:

UNITED STATES PATENTS Number Name Date 2,002,425 Williams May 21, 1935 2,921,877 Kolkmann Nov. 19, 1935 2,264,068 Buchard Nov. 25, 1941 OTHER. REFERENCES Radio Test Instruments, by Rufus P. Turner, ZiiT-Davis Publishing 00., New.Y0rk,'N. Y., 1946.

Emergency Ohmeter, by A. P.. Nielson, Radio News, Jan. 1945, page 219. 

